(I can’t immediately find out what happened to F20.7 – maybe it suffered the same fate as floor number 13 in New York skyscrapers)

The aetiology of schizophrenia is unknown; as this is the case we are forced to define schizophrenia on the basis of a number of symptoms which appear together sufficiently frequently to merit a grouping.In this way schizophrenia is a syndrome rather than a disease.A disease is a disorder with a specific cause and recognizable signs and symptoms whereas a syndrome is combination of signs and/or symptoms that form a distinct clinical picture.The ICD-10 classification system deliberately avoids including aetiology in its definition.

Schizophrenia is a disorder which covers a wide range of cognitive, emotional and behavioural disturbances; there is disintegration in the process of thinking, of contact with reality and a pattern of emotional unresponsiveness.

ICD-10 puts it nicely:

The schizophrenia disorders are characterized in general by fundamental and characteristic distortions of thinking and perception and by inappropriate or blunted affect.

There is no one sign that ‘guarantees’ a diagnosis of schizophrenia.For instance many of the characteristic symptoms of schizophrenia can occur during a manic phase of bipolar disorder or during psychotic depression.However the following ‘fundamental and characteristic disorders of thinking and perception’ are considered to have special importance in the diagnosis of schizophrenia.They are based on Schneider’s first rank symptoms, proposed in 1959 and are:

(c) hallucinatory voices giving a running commentary on the patient’s behaviour, or discussing the patient among themselves, or other types of hallucinatory voices coming from some part of the body;

(d) persistent delusions of other kinds that are culturally inappropriate and completely impossible, such as religious or political identity, or superhuman powers and abilities (e.g. being able to control the weather, or being in communication with aliens from another world);

(e) persistent hallucinations in any modality, when accompanied either by fleeting or half-formed delusions without clear affective content, or by persistent over-valued ideas, or when occurring every day for weeks or months on end;

(f) breaks or interpolations in the train of thought, resulting in incoherence or irrelevant speech, or neologisms;

(h) “negative” symptoms such as marked apathy, paucity of speech, and blunting or incongruity of emotional responses, usually resulting in social withdrawal and lowering of social performance; it must be clear that these are not due to depression or to neuroleptic medication;

(i) a significant and consistent change in the overall quality of some aspects of personal behaviour, manifest as loss of interest, aimlessness, idleness, a self-absorbed attitude, and social withdrawal.

(Source of (a)-(i) ICD-10)

The final thing to say is that the conception of schizophrenia is to a certain extent historical and many textbooks choose to explain schizophrenia as a disorder with reference to the history of its classification.The term itself was Bleuler introduced the term in his 1911 book ‘Dementia praecox or the group of schizophrenias’